Substrates coated in this way, having a high metallic reflection and a relatively low light transmission, are very decorative. In architecture they are often used for dressing walls, or curtain walling (glazing panels or facing tiles), as mirror elements, as semitransparent mirrors or as decorative glass sheets. They may also be provided with an additional decorative glass sheets. They may also be provided with an additional decorative printing and/or may also be used, where appropriate, in curved or deformed form. If they are used as monolithic glass panes, the surface layer is exposed, to the atmosphere in such a way that it must have a particularly high capacity to resist atmospheric effects. For safety reasons and/or for the purpose of increasing their flexural strength and their impact strength, the coated glass substrates intended for these applications are often thermally prestressed, that is to say heated to a temperature above 500° C., 550° C. or 600° C., and then very rapidly cooled. The reflecting multilayer coating comprising thin layers must also withstand this thermal stressing without being damaged, the properties, in particular the esthetic, optical, thermal and energy properties, of the coated glass glazing having not to be disturbed thereby.
A glass pane with a high thermal resistance is known, from document EP 0 962 429 A1, which has a multilayer coating of the kind mentioned at the beginning and which meets these requirements. In the case of this known multilayer coating, the dielectric base layer is composed of SiO2, Al2O3, SiON, Si3N4 or AlN, or else a mixture of at least two of these materials. All these materials can be applied to the glass pane only with a relatively low sputtering rate and/or only with a relatively high technological effort being supplied. Because industrial coating plants operate, for economic reasons, at run speeds as high as possible, the base layer can be applied, in the case of standard plants, only with a relatively small thickness. However, a larger thickness of the base layer may be desirable as an interference layer to modify the appearance in light reflection (color and intensity of the color) of the glass pane, both in terms of light reflection on the glass side and in terms of light transmission.
A multilayer coating capable of being curved and/or stressed beforehand, having a chromium layer as reflection layer, is also known from the document EP 0 436 045 A1. In this case, however, the covering layer is composed of an alloy of Al with Ti and/or Zr. Thanks to a top layer of this kind, the high reflectivity of the chromium layer on the layer side is lost and the reflection on the glass side reaches a maximum value of 50%. The base layer in this case is composed of TiO2, Ta2O5, ZrO2 or SiO2. Admittedly, the base layer must, in this case, be able to be deposited with a thickness such that it acts as a color-modifying interference layer, the increase in the layer thickness being, however, limited for these materials for technological and economic reasons.
Document EP 0 536 607 B1 describes coated glass panes with a metallic appearance, the transparent coatings of which are also suitable for a heat treatment. In this case however, the layer having metallic properties is composed of a metal compound, namely a metal boride, a metal carbide, a metal nitride or a metal oxinitride. These metal compounds do not possess the same gloss in light reflection as purely metal layers. Deposited on this layer is a protective metal layer, for example made of chromium, which is oxidized during the heat treatment. The multilayer coatings described in this publication are, firstly, coatings with a high transparency and the use of metallic reflection on both sides of the glass panes for decorative reasons plays no role in the case of these multilayer coatings.
It is desirable to ensure that the impression of color of the light reflected by interferential action of the base layer is adjustable in a targeted manner, without it being necessary in this case to perform technological feats or to reduce the run speed of the glass pane in a coating plant working continuously. A multilayer coating of this kind should have a high corrosion (mechanical, chemical) resistance and a high hardness and should maintain, after a heat-treatment process of the bending, toughening or annealing type, its properties, in particular a high light reflection, to be essentially neutral in color on the layer side and to have a transmission lying within the range between 2 and 15%.